How many minutes is the maximum permissible time for ground operations with DC power only?

The maximum permissible time for ground operations with DC power only is 5 minutes. This limitation is established to prevent battery depletion and ensure that the aircraft's electrical systems function correctly. When operating on DC power alone, the inverter is not in play, and relying solely on the battery can result in its rapid discharge if used beyond the specified time limit.

This limitation is crucial for maintaining electrical integrity and for ensuring that there is enough power available for essential systems during taxi or other operations before the engines are started. Adhering to this limitation helps to ensure smooth operation, prevents unnecessary battery wear, and allows for the proper function of critical systems when required, especially during the startup sequence of the aircraft.